Process of recovering helium



March 10, 1925. Y 1,529,625 J. A. RAFFERTY ET AL J v PROCESS OFRECQVERING HELIUM I Filed June 15, 1923 I5 Sheets-Sheet l 5 sneaks-sheets J. A. RAF-FERTY ET AL PROCESS OF REGOVERING HELIUH Filed June 15, 1923Mitch 10; 1925.

1 Patented Mar. 10, 1925.

- ,UNITED STATES PATENT "O F C Jmns A. nmnnrzor RYE, New YORK,ANDIHAROLDEL rnourson, ofcum-' IDENDT, WEST VIRGINIA, ASSIGNORS TOCARBIDE AND CARBON OHEKIG'ALS COR- PQBATIONZ A. CORPORATION OF NEW YORK.

PROCESS OF RE COVERII IG *HELIUM.

Application filed June is, 1923. Serial no. 645,872.

To all whom it may concern:

Be it known that we, JAMES A. RAFFERT and HAROLD 'E. THOMPSON, citizensof the United States, residing at Rye and Glen- 6 denin, in the countiesof Westche'ster and Kanawha and States of New York and West ,Virginia,respectively, have invented certain new and useful Improvements inProcesses of Recovering Helium, of which the 10 following is aspecification.

' The invention is a process for the separation of helium from gasmixtures. It will be described in connection with the recovery of heliumfrom a natural as containing such 16 proportions of hydrocar ons thateither the entire gas or the residue left after the helium extractlon isadapted for use as fuel, but

it will be understood that muchof the procedure to be described is alsoapplicable to 201 gas mixtures of quite different composition; y orexample to natural gases containing'so much'nitrogen as to be of littleor'no use as fuels, and to mixtures containing helium with hydrogen orairor both and resulting "from the intentional or accidental dilution ofhelium during its use for aeronautical purposes. Operating on a naturalgas containing hydrocarbons but in too small quan- .tities to fit thegas for use as a fuel, the process will produce, as a by-product, agombustible. gas containing the hydroear= ons. 1 Only one plant capableof producing helium in quantities suflicient for aero- .'the NavyDepartment plant whic is now in successful operation at Fort Worth,Texas.

The present invention will be described as.

venient to consider the hy rocarbons collectively as a relativelynon-volatile fraction of the gas. It should be noted that the gasnautical use has ever been set up this being Since methane a is treatedfor gasolene-extraction before it.

reaches the helium plant and hence is almost free from butane and less.volatilehy f drocarbons. The process and apparatus to;

be described are designed for. the treatment of a material which 'doesnot contain more than small quantities 'ofgasolene constit} uents, andwell-known rocesses -may be preliminarily applied, -.w ere necessary, tosecure thisconditlon.

Heliumresists liquefaction more strongly gas and hence is than any otherknown eof easily the most volatile material in thenat= ceived :at theplant .by pipe-line under a pressure which fluctuatessomewhat butrare--" lfy or never falls belowv 10 atmospheres. The

ural gas. Hydrogen is: absent from the gas, and nitrogen, boiling atxabout 193 C. under 760 mm. pressure stands nextto-the. y

rmer practice included an initial expansion of the. s to substantiallybarometric.

pressure wit out utilization of the energy represented by the pressureon the gas.

Since several million cubic feet of gas were treated. daily, a] veryconsiderable energy I loss was sustained in this way.

The gas was then scrubbed with a solu-f tion of an alkaline substance,such as limewater, to reduce the carbon dioxid content in order to-prevent the clogging of the helium apparatus by congelation of thecarbon dioxid. i

A portion of the gas-was then compressed to about. 6. atmospheres, therest of the gas bein brought to a much higher pressure, usua lyconsiderably in excess of atmospheres. Both portions of compressed gaswere cooled, eventually by heat-exchange with. waste gases, and passedto a column,- the-.niixture passed through a series of provelydecreasing temperatures for the separation 'of successive fractions ofthe hydrocarbons and the nitrogen.

mo During this stage of the process, the;na.tural gas undergoingtreatment was held ansion to -pressure furmshed most scribed, operatingtiall pure 1i uid auxi iary cyc e.

amount of material within the condensers.

The last condenser of the series just deat about 6 atmos )heres wascooled with su stannitrogen provided by an Two other condensers atinternal pressure,

higher temperatures the last condenser, and another condenser cooled bythe reflux condenser and hence operatin at the highest temperature ofall. In ad ition, a. large was liquefied before the first condenserwasreached, at the expansion of the high-pressure as.

/With pressures of on y, 6 atmospheres within the condensers, it wasnecessary to rmit the cooling liquids surrounding them to boil atsubstantially atmospheric pressure The series of steps just describedproduced a helium concentrate containing usuup to atmospherictemperature.

' liquefaction of steps whi allyabout 60% helium, though about 7 5% wastheoretically possible under optimum conditions. ThlS concentrate,containing only helium and nitrogen, was then expanded to atmosphericpressure and allowed to warm This concentrate was then. com ressed toabout atmospheres and coole to the temperature of bo1lmg nitrogen,whereupon sufiicient of nitrogen was in the helium concentrate toincrease the helium content to 95% or more.

In accordance with our invention, the process described above has beenso modified that the ower consumption is reatly reduced elium which isof hi er urity may also be produced, and by .t e a dition e have nocounterpart inthe rior process, the helium content can be so increasedthat impurities are either entirely negligible or absent. The process isalso improvedin several other respects, notablyin the greater ease withwhich the desired ressuies, and hence qualtemperatures and heliumproduced, can be ity and quantity 0 maintained.

The invention will now be "explained in connection with the accompanyingdrawing, in which- Fig. 1 is a series of curves showing the theoreticalhelium conten or test at various presure's (plotted as abscissae) andwere used, an inter medlate condenser cooled by the reflux fromfrom theintermediate through brought about at three different temperatures,- allreadily obtainable by the evaporatlon of liquid nitrogen at or nearatmospheric pressure;..

Fig. 2 is a curve showing the reduction in helium test which follows anincrease of temperature from 190 C. to -185 0., at

VfillOllS 0011111111. pressures;

Fig. 3 is a diagrammatic representationof our improved process; an

Fig. 4: shows an auxiliary purifier containing activated carbon.

Figs

. land 2 show strikingly the reason for certain instabilities inoperation which vwere encountered in the prior process.

Fig. 1, the prior operating pressure of 6 atmospheres is on the steeperportion of each curve, variation in pressure is to alter the test of theoutlet helium concentrate materially. Similarly, Fig. 2 shows that evena slight increase in condenser temperature, such as may result from aslight contamination of the nitrogen bath with methane, will seriouslyaffect the test of the helium.

In accordance with our invention, the operations formerly carried outunder a pressure of about 6 atmospheres are conducted at higherpressure, corresponding to'a point beyond the knee of any of the variouscurves inFigs. 1 and 2. In this region, all the curves have relativelylow slopes, and the effect of fluctuations in temperature and pressureis considerably mitigated.

As lessand less advantage is obtained by successive increasesinpressure, it will be seen that a practical pressure limit is soonreached. We have found that a working pressure of about 22 atmospheresgives conso that the eifect of any inadvertent siderably better resultsin the respect just 7 discussed than 6 atmospheres.

The use of such 'a pressure as 22 atmosabout 160% to about 90%, withoutthe use of lower temperatures than before. In fact,

' certain ofthe condensers may be held at considerably highertemperatures than formerly, these higher temperatures bein such as thoseproduced by boiling liqui s. of composition similar to those atpressures approximating 17 atmospheres instead of the substantiallyatmospheric pressure formerly maintained. This latter ives rise to aprincipal advantage of-our 1nvention,in that the gas produced babullition of these liqulds 1s at a su icient pressure to enter the pie-line without. any

work being done on it a er it has been used for cooling.

The curves of Fig. 1 also show that the final condensation of impuritiesfrom the does the former pressure of formerly used, but

the

impure helium, formerly conducted at about 70 atmospheres, can becarried out at very much lower pressures, even at the 22 atmospheresused in. the earlier stages, and a higher test helium neverthelessproduced, provided a temperature only a little lower than that nowemployed is maintained at the condenser. Such a temperature is readilyattained by evaporating nitrogen under a partial vacuum, say at aboutone-half atmosphere absolute pressure.

Our preferred arrangement for the complete process is shown in Figs. 3and 4, and Is as follows:

The helium-bearing gas, previously des prived of its gasoleneconstituents, and arriving at the plant through a pipe-line 1, at orabove 10 atmospheres pressure, is scrubbed at that pressure inscrubber'2 for the re-- moval of carbon dioxid. Owing to the increasedsolubility of carbon dioxid at such pressures, water alone acts as avery'efi'ective agent for removing carbon dioxid. If a more completeremoval of carbon-dioxid than can be obtained with water alone isdesired, the gas may be passed to a second scrubber 3, where it istreated with a solution of an a'lkalinesubstance such as lime water. Theabsorbent action of lime water is also increased by the pressure.

From scrubber 3 a portion of the gas passes through line 4 to lowpressure compressor 5 where its pressure is brought to about 23atmospheres. The compressed gas passes through a fore-cooler 6 refrierated by an ice machine 7, andthence through line 8 to the mainheat-exchan er.

Another portion of the he ium-bearing 1 gas, after removal of the carbondioxid. is

{ byline 17. passes through a coil 18 likewise drawn through line 9 tohigh pressure 1nulti stage compressor 10, and is brought to about 135atmospheres. The high pressure. gas passes through a fore-cooler 11refri erated by an ice machine 12, and is carried t rough line 13 to themain heat-exchanger, but is kept separate therein from the low pressuregas entering through 8.

The high pressure gas emerges from the heat-exchanger through line 14,whence it passes to coil 15 immersed in a bath of boiling liquid at lowtemperature. After its final cooling in this cm], the high pressure gasexpands through valve 16 into the column at: a point below condenser A.The low pressure gas leaves the heat-exchanger immersed in a lowtemperature bath of boiling liquid, and then flows through line 19 andvalve 20 tothe same column into which the high pressure gas is expanded.

The expansion of the cooled high pressure gas to the column pressure,about 22 atmospheres, absorbs a large quantity of heat. The lessvolatile constituents of both high and low pressure gas, for example thepropane, most of the ethane and some methane,

are condensed, flow down through the column where they are sub'ected torectification to remove any disso ved helium, and

collect in the kettle containing the coil 15..

Those constituents of the gas which are notliquefied on expansion, andincluding all the helium of the. gas, pass upwardly through the columnto condenser A, where they are subjected to the temperature of theliquid boiling about the condenser, thisliquid being held under apressure of about 17 atmospheres. A further quantity of relativelynon-volatile material is liquefied in condenser A and returns to thecolumn below, in which it also is rectified. The helium and other gasesnot liquefied in condenser A pass through .line 21 to :1

column which is surmounted by condenser q B. Condenser B 1s surroundedby a boiling liquid which'is held at the same pressure as that whichobtains about the'condenser A, but the liquidsurrounding condenser 13contains more of the volatile constituents of the natural gas, such asnitrogen and ture than the liquid about the condenser A. As a result, anadditional quantity of ma-J terial is liquefied in condenser. B anddemethane, and hence is at a lower temperascends through and isrectified in the column column which is immediately below condenser C,the helium-containing mixturebeing still at the same pressure of 22atmospheres. Condenser O is cooled by substantially pure liquid nitrogenboiling at about atmospheric pressure, and hence the tem-- perature ofcondenser C- approaches closely the boiling point of nitrogen, -193 C.As this temperature is conslderably' below the temperatures ofcondensers A and B, afurther quantity of the gas associated with thehelium, nowchiefly nitrogen, is condensed, and passes down through thecolumn immediately below, where it is rectified to remove any dissolvedhelium. The liquid col lects in kettle 24 at the bottom of the column:

the coil 18 and there surrounds and. cools coil 25, which presently tobe decontaining about 90% of helium will be produced. This concentratepasses through. I

. line 26 to the final condenser D where itis subjected, still at apressure of about 22 atmospheres, to the temperature of nitrogen boilingunder reduced pressure, say at about one-half atmosphere absolute. rThis ,will

give a temperature below ,195 C. in con denser D, and as a'result someof the small amount of residuah nitrogen will be liquecooler 32refrigerated it boils away continuously fied and aconcentrate containinabout 98% helium, and usually consi ered pure enough for aeronauticalpurposes, will pass the condenser, expand through valve 27 ,and

pass through line 28 to the helium holder 29.

The arrangement for producing the nitrogen baths which surroundcondensers C and D will now be described.

Nitrogen is drawn from holder 30 and compressed in multi-stagecompressor 31 to a pressure of about 135 atmospheres. The compressed gasthen passes through foreby the ice machine 33, and thence through thenitrogen heat-exchanger. The cooled high pressure nitrogen emerges fromthe heat-exchanger through line 33 and passes through coi 25 previouslyreferred to,.where it is brought into thermal contact with ing liquid inkettle 24. The liquid in kettle 24, it will be noted, is under apressure of about 22 atmospheres. The nitrogen now passes through coil34 disposed in the'bath around condenser G and hence immersed innitrogen boiling at or a little above atmosph'eric pressure.

After this final cooling the nitrogen expands through valve 35, whichresults in its partial liquefaction. The liquid nitrogen collects aboutcoil 34 in condenser C, where and produces the refrigerating eflectalready referred to. The gaseous nitrogen produced by the boiling ofthis bath passes at slight pressure through line 36 to the nitrogenheat. exchanger, where it cools the high pressure nitrogen and thenflows through line 37 to the nitrogen holder 30.

The space around condenser D is held, as alread stated, under a partialvacuum.

Liqui nitrogen will rise at a regulated rate throu h valve '38 andcollect about condenser D, boiling there under the reduced pressure at avery low temperature. Y The gaseous nitrogen producedby the boiling ofthis liquid passes through line 39 to another section of the. nitrogenvheat-exchanger, where it asslsts in the cooling of the high. pressurenitrogen, and then passes through line 40 and vacuum ump 41 to thenitrogen holder. The smal quantity of liquid formed in condenser D andconsisting of pure nitrogen,

returns through the trap 42 to the top of the column surmounted bycondenser C.

I The gases produced by the boiling liquids around condensers A and Bpass through lines 43 and 44 'resplectively to the main heatexchanger,where t ey cool the high and low pressure helium-bearing gas, and thenpass through lines 45 and 46 respectively to a receiver which dischargeshehum -free' gas into a plpe-hne to be transportedto-the place of itsconsum tion. Since the baths about condensers and B are maintained at 17atmospheres-pressure, and the reverse flow line already "with theexception the very cold D011" passagesof the main heat-exchanger are atthe same, pressure, the exit 1glases may enter the line without beingfurt er compressed. A portion of the liquid contained in the kettlearound coil 15 is also continuously withdrawn through line 47 to themain heat-exchanger, in which it evaporates and assists in cboling thehigh and low pressure helium bearing gas, passing from theheat-exchanger through line 48 to the receiver and pipereferred to. Theexit gases passing through the main heat-exchanger and lines 45, 46iand48, constitute practi cally all the natural gas entering. the plant ofthe helium.

The condenser B is cooled by liquid which 1 collects in kettle 24, andflows through line 49 and valve 50 into the space surrounding condenserB. Condenser A is similarly cooled by liquid and flows through spacesurrounding condenser A. At valves 50 and 52, the pressure on theliquids just referred to is reduced from about 22 atmospheres to about17 atmospheres. Should it be desired to remove from the helium leavingcondenser D the very small quantity of impurities contained in it,'theapparatus shown in- Fig. 4 may be used bein introduced into the systemat an approprlate point, for exam le between condenser D and the heliumhol er.

This apparatus consists of a series of identical absorbers comprising anpacked with activated carbon 53 held between foraminous partitions 54.To facilitate' the absor tion of the impurity (nitrogen) inthe car 11.,the latter sli'ouldbecooled to a very low temperature and we have shownthe absorbers provided with jackets 55, through which may bepassed avery cold medium, such as nitrogen from the space around condenser G.The absorbers maybe small, as they are designed to take up an impuritywhich constitutes only about 2% of the helium, the helium being lessthan 1% of the gas treated.

When cooled to a temperature such as that indicated, activated carbonselectively .ab-

(1 to any desired value. When one absorber is saturated to the desireddegree with impurity, it is cut out of both the helium and therefrigeration circuits and allowed to warm up to room temperature, theabsorbed impurity will pass of! through which collects in kettle 22,line 51 and valve 52 to the inner chamber.

sorbs the impurity with great efliciency, and 1 the-purity of the heliumcan be raise whereupon 56. The absorber is then ready for use again tothe required whereas in the prior process all the gas was compressedtwice, and each time from atmospheric pressure, while the 60% heliumconcentrate was additionally compressed from atmospheric pressure to 70atmospheres. As a result, fewer compressors are required and less poweris consumed.

Helium of greater purity is roduced even without the activated carbon asorber. The latter, at the low temperature used by us, affords a means.for securing helium of any desired purity.

The carbon dioxid may be removed from i the gas more effectively, insmaller apparamaterial, can be smaller, as the gas is considerablyreduced in volume by the higher pressure. It is true that the gaspassing through condenser D is at lower pressure than in the final 70atmosphere condenser of the prior process, but only about 1% of the gastreated flows through this condenser. Furthermore, the urity of thehelium passing to D is muc higher than in the former process, so thatcondenser D' treats less gas than before.

The process is less sensitive to changes in operating conditions. Thesaving in power consumption in th new process is estimated at As alreadystated, the gas mixture passin through "condenser C will contain as bigas 90% helium. In other words, the temperature and pressure conditionsprevailing in the condenser are such that the partia pressure of the imurities does not exceed 10% of the tota pressure. Our invention is notto this condition, however, and we regard as within our inthe pipe-line.

vention all methods of o eration "wherein d with a temperature not elow193 C. thereis apphed a pressure suflicient to cause the partialpressure of the impurities to be not more than 20% of the totalpressure.

In our novel process, all the principal cooling baths are held at suchpressures as willpermit of the gases produced by their ebullition beingintroduced directly into Any usual pipe-line pressures, for example 10to 20 atmos heres, are adapted for use in our 'inventlon at the pointsreferred to, and are covered in the appended claims.

Having now described our invention, we claim:

1. Process of producing a helium concentrate from natural gas whichcomprises liquefying a portion of the gas, holding the liquid soproduced under a pipe-line pressure, and cooling another portion of thegas under higher pressure therewith, said higher pressure being suchthat partial liquefaction of the ortion so cooled'will result.

2. Process 0 producing a helium concentrate from natural gas whichcomprisw progressively cooling the gas by means of liquefied fractionsthereof boiling at a pipeline pressure, while holding the gas to becooled Tunder suflicient pressure to liquefy non-helium constituentsthereof.

3. Process of producili a helium concen successive steps of compressing,cooling, and expanding the gas to-liquefy a portion thereof, leaving agaseous residue and liquefying a portion of said residue y transferringheat therefrom to natural-gas constituents held atpipe-line ressure.

- trate from natural gas w ich comprises the In testimony w erebf, weaflix our signatures. 1

JAMES A. RAFFERTY. HAROLD E. THOMPSON.

